Known from German Patent DE 196 21 449 is a device with which a vibratory fill-level limit switch can be operated. The limit switch includes a vibration resonator, which is connected in the feedback branch of a self-excitable transducer system with amplifying arrangement. In such case, a piezo-element is provided in the vibration resonator, both for exciting oscillation and for oscillation detection. The exciter signal of the amplifying arrangement, with which signal the piezo-element is excited to oscillate, involves periodic, rectangular signals. During the edges of the exciter signal, the piezo-element undergoes charge reversal, and this leads to charge-reversal signals in the response signal. The circuit presented in the Patentschrift has the task of removing these charge-reversal signals and of minimizing the duration of the charge-reversal process. For this task of signal removal, a control circuit is presented, which is controlled by the exciter signal and which decouples the output of the piezo-element from the amplifier arrangement. The minimizing of the duration of the charge-reversal process is achieved by a charging current control circuit, which produces a virtual reference. Both circuits contain, among other things, operational amplifiers and a semiconductor switch. Disadvantageous in this device is that the aforementioned components are relatively expensive.